Light emitting devices are being used in a variety of applications. The suitability of a particular light emitting device embodiment is often a function of the projected light emission pattern. For example, automotive lamps commonly require that the light emitting device provide a light emission pattern that conforms to a given standard. In like manner, consumer applications, such as a flash element on a camera or phone device, require a substantially uniform lighting of the target image.
The quality of a given light emitting device with regard to satisfying an expressed or implied light output pattern consistency is dependent upon a variety of factors, including the alignment of the light emitting element and the lens element that provides the desired light output pattern. A misalignment of the lens element and the light emitting element may, for example, cause certain areas of a camera image to appear darker than other areas, or cause an automotive lamp to fail standards testing.
A variety of techniques are commonly used to accurately align a lens element to a light emitting element as the lens element is situated with respect to the light emitting element. For example, highly precise pick-and-place machines may be used to place each lens element at a given position relative to a light emitting element that is mounted on a substrate. In some attachment processes, an optical element on the pick-and-place machine detects the center of the light emitting element; in other processes, physical alignment features are provided on the substrate upon which the light emitting element is mounted.
However, even after the accurate placement of the lens element with respect to the light emitting element, it is often difficult to maintain their alignment during the subsequent manufacturing processes encountered in the fabrication of the finished product. Typically, the lens element is accurately positioned on the substrate that contains the light emitting element and attached via an adhesive element that is subsequently cured to fixedly attach the lens element to the light emitting element. The adhesive element also serves to isolate the light emitting element from external elements by forming a seal that surrounds the light emitting element. A number of factors, however, may affect the initially accurate alignment of the lens element and the light emitting element.
The uncured adhesive, such as an epoxy or silicone, may have low viscosity, and during the transportation of the attached lens element to the light emitting element to the equipment (e.g. oven) that cures the adhesive, excessive mechanical impact and handling may move the lens element.
Similarly, adhesives such as epoxy and silicone that are cured thermally will shrink when the crosslink (cure) occurs, which may introduce a shift in the location of the lens element relative to the light emitting element.
In like manner, air that may be trapped inside the lens element during the lens element attachment process may exert non-uniform forces that cause a shift in the position of the lens element; and, during the cure of the adhesive, which usually involves heat, the trapped air will likely expand and create steam pressure inside the lens element, which may also introduce an unpredictable force that may alter the lens element's position relative to the light emitting element.
Each of these potential movements of the lens element, and other factors, will likely introduce a misalignment of the lens element and the light emitting element.